1. Field of the Invention
This invention relates to improvements relating to a tubular lock and a master key,
2. Description of the Related Art
Tubular locks have been used commonly in places, such as recreational and amusement centers, where a large number of similar pieces of equipment, e.g., amusement and game machines, are provided. Management of such a large number of machines in such places is difficult and troublesome. Generally, the machines are provided with respective tubular locks, and respective keys for the tubular locks are kept in a bundle and managed by an operator. When one of the machines requires unlocking, the operator in charge of the keys must select the right key from the bundle of keys according to an item number provided on the particular machine to be opened. However, if one of the keys has been misplaced or removed from the key bundle and not returned, the corresponding machine cannot be opened. In order to facilitate management of such keys, there is suggested a master key which can be used to open a plurality of similar or identical machines provided within a particular area.
Referring to FIG. 1, a conventional master key 1 includes a key base 11, a key tube 12, seven slide pieces 13 (only one is shown), seven key springs 14 (only one is shown), a sleeve 15, an elastic member 16 and a screw 17.
The key base 11 has a front end which is recessed to form a receiving space ill and seven spring slots 112 around the receiving space 111. The key tube 12 is inserted into the receiving space 111, and includes a central hole 122 defined by a tubular wall 121 and seven grooves 123 formed on an outer surface of the tubular wall 121.
Each slide piece 13 is placed slidably within one of the grooves 123, and each key spring 14 is inserted into one of the spring slots 112 to abut against the corresponding slide piece 13. The sleeve 15 is sleeved on the key tube 12 to retain the slide pieces 13 in the respective grooves 123. The elastic element 16 is sleeved on the key tube to bias the sleeve 15. The screw 17 is used to fasten the key tube 12 to the key base 11.
Referring to FIG. 2, a conventional tubular lock 2 includes a lock housing 21, a rotatable core body 22, a fixed body 23, and several sets of outer and inner tumblers 24, 25 and tumbler springs 26.
The lock housing 21 includes a key hole 211 for insertion of the key 1. The core body 22 is disposed inside the lock housing 21 and includes a plurality of first tumbler holes 221. The fixed body 23 is fixed within the lock housing 21 and has a plurality of second tumbler holes 231 in alignment with the first tumbler holes 221. The second tumbler holes 231 are formed as blind holes with equal depth.
The outer tumblers 24 are different in length, whereas the inner tumblers 25 have an equal length which is the same as the depth of the second tumbler holes 231. Each tumbler spring 26 biases one of the inner tumblers 25. Before the master key 1 is inserted into the tubular lock 2, the outer and inner tumblers 24, 25 are biased by the respective tumbler springs 26 to move toward the key hole 211 so that each inner tumbler pin 25 projects out of the lock seat 23 and into the core body 22.
Referring to FIG. 3, when the master key 1 is inserted into the tubular lock 2, since the spring force of each key spring 14 is larger than that of the tumbler springs 26, each slide piece 13 pushes the outer and inner tumblers 24, 25 until the inner tumblers 25 contact the bottoms of the respective second tumbler holes 231. With the continued insertion of the master key 1, as the outer and inner tumblers 24, 25 cannot move further, the slide pieces 13 are pushed backward until the front end of the key tube 12 presses the core body 22. At this time, the juncture between the outer and inner tumblers 24, 25 coincides with the juncture between the core body 22 and the fixed body 23 so that the core body 22 is released and becomes rotatable.
However, the aforesaid tubular lock 2 and the master key 1 encounter the following problems:
1. Assembly is inconvenient due to a large number of components used in the master key 1. In particular, since the sleeve 15 and the key base 11 are separate components, assembly must be done by attaching the sleeve 15 and the elastic element 16 to the key tube 12 after the slide pieces 13 are put into the respective grooves 123, and by aligning carefully the slide pieces 13 with the respective key springs 14 in order to insert the slide pieces 13 into the respective spring slots 112. Assembly as such is complicated, increases costs, and consumes time and labor.
2. All of the inner tumbler pins 25 must be equal in length in order to ensure that they do not protrude from the fixed body 23 when they are pressed to reach the bottoms of the respective second tumbler holes 231 in order to permit rotation of the core body 22. However, it is easy for a burglar to pick the tubular lock 2 by inserting and pushing seven pins into the first tumbler holes 221, respectively. Therefore, the tubular lock 2 and the master key 1 do not provide a sufficient anti-burglar effect.